参考
AVCaptureSession是AVFoundation的核心类,用于捕捉视频和音频,协调视频和音频的输入和输出流.

设置Session分辨率

- (BOOL)canSetSessionPreset:(AVCaptureSessionPreset)preset;

@property(nonatomic, copy) AVCaptureSessionPreset sessionPreset;

实例：

// 2 设置session显示分辨率
 if ([[UIDevice currentDevice] userInterfaceIdiom] == UIUserInterfaceIdiomPhone)
    [session setSessionPreset:AVCaptureSessionPreset640x480];
else
    [session setSessionPreset:AVCaptureSessionPresetPhoto];

给Session添加input输入

#获取session的输入设备
@property(nonatomic, readonly) NSArray<__kindof AVCaptureInput *> *inputs;

- (BOOL)canAddInput:(AVCaptureInput *)input;
- (void)addInput:(AVCaptureInput *)input;
- (void)removeInput:(AVCaptureInput *)input;

实例：

AVCaptureDevice *device = [AVCaptureDevice defaultDeviceWithMediaType:AVMediaTypeVideo];
AVCaptureDeviceInput *deviceInput = [AVCaptureDeviceInput deviceInputWithDevice:device error:&error];

isUsingFrontFacingCamera = NO;
if ([session canAddInput:deviceInput]){
    [session addInput:deviceInput];
}

给session添加output输出

@property(nonatomic, readonly) NSArray<__kindof AVCaptureOutput *> *outputs;

- (BOOL)canAddOutput:(AVCaptureOutput *)output;
- (void)addOutput:(AVCaptureOutput *)output;
- (void)removeOutput:(AVCaptureOutput *)output;

Session的开启与停止

AVCaptureSession 最后必须开启才能使用

- (void)startRunning;
- (void)stopRunning;

//是否正在Running
@property(nonatomic, readonly, getter=isRunning) BOOL running;